Initial checkin of the LLVM source-level debugger. This is still not finished,

by any stretch of the imagination, but it is pretty cool and works :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10685 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 911 insertions, 0 deletions

diff --git a/lib/Debugger/UnixLocalInferiorProcess.cpp b/lib/Debugger/UnixLocalInferiorProcess.cpp
new file mode 100644
index 0000000..ff9a15a
--- /dev/null
+++ b/lib/Debugger/UnixLocalInferiorProcess.cpp
@@ -0,0 +1,911 @@
+//===-- UnixLocalInferiorProcess.cpp - A Local process on a Unixy system --===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+// 
+// This file provides one implementation of the InferiorProcess class, which is
+// designed to be used on unixy systems (those that support pipe, fork, exec,
+// and signals).
+//
+// When the process is started, the debugger creates a pair of pipes, forks, and
+// makes the child starts executing the program.  The child executes the process
+// with an IntrinsicLowering instance that turns debugger intrinsics into actual
+// callbacks.
+//
+// This target takes advantage of the fact that the Module* addresses in the
+// parent and the Module* addresses in the child will be the same, due to the
+// use of fork().  As such, global addresses looked up in the child can be sent
+// over the pipe to the debugger.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Debugger/InferiorProcess.h"
+#include "llvm/IntrinsicLowering.h"
+#include "llvm/Constant.h"
+#include "llvm/Module.h"
+#include "llvm/ModuleProvider.h"
+#include "llvm/Type.h"
+#include "llvm/iOther.h"
+#include "llvm/ExecutionEngine/GenericValue.h"
+#include "llvm/ExecutionEngine/ExecutionEngine.h"
+#include "Support/FileUtilities.h"
+#include "Support/StringExtras.h"
+#include <cerrno>
+#include <unistd.h>        // Unix specific debugger support
+#include <sys/types.h>
+#include <sys/wait.h>
+using namespace llvm;
+
+// runChild - Entry point for the child process.
+static void runChild(Module *M, const std::vector<std::string> &Arguments,
+                     const char * const *envp,
+                     FDHandle ReadFD, FDHandle WriteFD);
+
+//===----------------------------------------------------------------------===//
+//                        Parent/Child Pipe Protocol
+//===----------------------------------------------------------------------===//
+//
+// The parent/child communication protocol is designed to have the child process
+// responding to requests that the debugger makes.  Whenever the child process
+// has stopped (due to a break point, single stepping, etc), the child process
+// enters a message processing loop, where it reads and responds to commands
+// until the parent decides that it wants to continue execution in some way.
+//
+// Whenever the child process stops, it notifies the debugger by sending an
+// character over the wire.
+//
+
+namespace {
+  /// LocationToken - Objects of this type are sent across the pipe from the
+  /// child to the parent to indicate where various stack frames are located.
+  struct LocationToken {
+    unsigned Line, Col;
+    const GlobalVariable *File;
+    LocationToken(unsigned L = 0, unsigned C = 0, const GlobalVariable *F = 0)
+      : Line(L), Col(C), File(F) {}
+  };
+}
+
+// Once the debugger process has received the LocationToken, it can make
+// requests of the child by sending one of the following enum values followed by
+// any data required by that command.  The child responds with data appropriate
+// to the command.
+//
+namespace {
+  /// CommandID - This enum defines all of the commands that the child process
+  /// can respond to.  The actual expected data and responses are defined as the
+  /// enum values are defined.
+  ///
+  enum CommandID {
+    //===------------------------------------------------------------------===//
+    // Execution commands - These are sent to the child to from the debugger to
+    // get it to do certain things.
+    //
+
+    // StepProgram: void->char - This command causes the program to continue
+    // execution, but stop as soon as it reaches another stoppoint.
+    StepProgram,
+
+    // FinishProgram: FrameDesc*->char - This command causes the program to
+    // continue execution until the specified function frame returns.
+    FinishProgram, 
+
+    // ContProgram: void->char - This command causes the program to continue
+    // execution, stopping at some point in the future.
+    ContProgram,
+
+    // GetSubprogramDescriptor: FrameDesc*->GlobalValue* - This command returns
+    // the GlobalValue* descriptor object for the specified stack frame.
+    GetSubprogramDescriptor,
+
+    // GetParentFrame: FrameDesc*->FrameDesc* - This command returns the frame
+    // descriptor for the parent stack frame to the specified one, or null if
+    // there is none.
+    GetParentFrame,
+
+    // GetFrameLocation - FrameDesc*->LocationToken - This command returns the
+    // location that a particular stack frame is stopped at.
+    GetFrameLocation,
+
+    // AddBreakpoint - LocationToken->unsigned - This command instructs the
+    // target to install a breakpoint at the specified location.
+    AddBreakpoint,
+
+    // RemoveBreakpoint - unsigned->void - This command instructs the target to
+    // remove a breakpoint.
+    RemoveBreakpoint,
+  };
+}
+
+
+
+
+//===----------------------------------------------------------------------===//
+//                            Parent Process Code
+//===----------------------------------------------------------------------===//
+
+namespace {
+  class IP : public InferiorProcess {
+    // ReadFD, WriteFD - The file descriptors to read/write to the inferior
+    // process.
+    FDHandle ReadFD, WriteFD;
+
+    // ChildPID - The unix PID of the child process we forked.
+    mutable pid_t ChildPID;
+  public:
+    IP(Module *M, const std::vector<std::string> &Arguments,
+       const char * const *envp);
+    ~IP();
+
+    std::string getStatus() const;
+
+    /// Execution method implementations...
+    virtual void stepProgram();
+    virtual void finishProgram(void *Frame);
+    virtual void contProgram();
+
+
+    // Stack frame method implementations...
+    virtual void *getPreviousFrame(void *Frame) const;
+    virtual const GlobalVariable *getSubprogramDesc(void *Frame) const;
+    virtual void getFrameLocation(void *Frame, unsigned &LineNo,
+                                  unsigned &ColNo,
+                                  const GlobalVariable *&SourceDesc) const;
+
+    // Breakpoint implementation methods
+    virtual unsigned addBreakpoint(unsigned LineNo, unsigned ColNo,
+                                   const GlobalVariable *SourceDesc);
+    virtual void removeBreakpoint(unsigned ID);
+
+
+  private:
+    /// startChild - This starts up the child process, and initializes the
+    /// ChildPID member.
+    ///
+    void startChild(Module *M, const std::vector<std::string> &Arguments,
+                    const char * const *envp);
+
+    /// killChild - Kill or reap the child process.  This throws the
+    /// InferiorProcessDead exception an exit code if the process had already
+    /// died, otherwise it just kills it and returns.
+    void killChild() const;
+
+  private:
+    // Methods for communicating with the child process.  If the child exits or
+    // dies while attempting to communicate with it, ChildPID is set to zero and
+    // an exception is thrown.
+
+    /// readFromChild - Low-level primitive to read some data from the child,
+    /// throwing an exception if it dies.
+    void readFromChild(void *Buffer, unsigned Size) const;
+
+    /// writeToChild - Low-level primitive to send some data to the child
+    /// process, throwing an exception if the child died.
+    void writeToChild(void *Buffer, unsigned Size) const;
+
+    /// sendCommand - Send a command token and the request data to the child.
+    ///
+    void sendCommand(CommandID Command, void *Data, unsigned Size) const;
+
+    /// waitForStop - This method waits for the child process to reach a stop
+    /// point.
+    void waitForStop();
+  };
+}
+
+// create - This is the factory method for the InferiorProcess class.  Since
+// there is currently only one subclass of InferiorProcess, we just define it
+// here.
+InferiorProcess *
+InferiorProcess::create(Module *M, const std::vector<std::string> &Arguments,
+                        const char * const *envp) {
+  return new IP(M, Arguments, envp);
+}
+
+/// IP constructor - Create some pipes, them fork a child process.  The child
+/// process should start execution of the debugged program, but stop at the
+/// first available opportunity.
+IP::IP(Module *M, const std::vector<std::string> &Arguments,
+       const char * const *envp)
+  : InferiorProcess(M) {
+
+  // Start the child running...
+  startChild(M, Arguments, envp);
+  
+  // Okay, we created the program and it is off and running.  Wait for it to
+  // stop now.
+  try {
+    waitForStop();
+  } catch (InferiorProcessDead &IPD) {
+    throw "Error waiting for the child process to stop.  "
+          "It exited with status " + itostr(IPD.getExitCode());
+  }
+}
+
+IP::~IP() {
+  // If the child is still running, kill it.
+  if (!ChildPID) return;
+
+  killChild();
+}
+
+/// getStatus - Return information about the unix process being debugged.
+///
+std::string IP::getStatus() const {
+  if (ChildPID == 0)
+    return "Unix target.  ERROR: child process appears to be dead!\n";
+
+  return "Unix target: PID #" + utostr((unsigned)ChildPID) + "\n";
+}
+
+
+/// startChild - This starts up the child process, and initializes the
+/// ChildPID member.
+///
+void IP::startChild(Module *M, const std::vector<std::string> &Arguments,
+                    const char * const *envp) {
+  // Create the pipes.  Make sure to immediately assign the returned file
+  // descriptors to FDHandle's so they get destroyed if an exception is thrown.
+  int FDs[2];
+  if (pipe(FDs)) throw "Error creating a pipe!";
+  FDHandle ChildReadFD(FDs[0]);
+  WriteFD = FDs[1];
+
+  if (pipe(FDs)) throw "Error creating a pipe!";
+  ReadFD = FDs[0];
+  FDHandle ChildWriteFD(FDs[1]);
+
+  // Fork off the child process.
+  switch (ChildPID = fork()) {
+  case -1: throw "Error forking child process!";
+  case 0:  // child
+    delete this;       // Free parent pipe file descriptors
+    runChild(M, Arguments, envp, ChildReadFD, ChildWriteFD);
+    exit(1);
+  default: break;
+  }
+}
+
+/// sendCommand - Send a command token and the request data to the child.
+///
+void IP::sendCommand(CommandID Command, void *Data, unsigned Size) const {
+  writeToChild(&Command, sizeof(Command));
+  writeToChild(Data, Size);
+}
+
+/// stepProgram - Implement the 'step' command, continuing execution until
+/// the next possible stop point.
+void IP::stepProgram() {
+  sendCommand(StepProgram, 0, 0);
+  waitForStop();
+}
+
+/// finishProgram - Implement the 'finish' command, executing the program until
+/// the current function returns to its caller.
+void IP::finishProgram(void *Frame) {
+  sendCommand(FinishProgram, &Frame, sizeof(Frame));
+  waitForStop();
+}
+
+/// contProgram - Implement the 'cont' command, continuing execution until
+/// a breakpoint is encountered.
+void IP::contProgram() {
+  sendCommand(ContProgram, 0, 0);
+  waitForStop();
+}
+
+
+//===----------------------------------------------------------------------===//
+// Stack manipulation methods
+//
+
+/// getPreviousFrame - Given the descriptor for the current stack frame,
+/// return the descriptor for the caller frame.  This returns null when it
+/// runs out of frames.
+void *IP::getPreviousFrame(void *Frame) const {
+  sendCommand(GetParentFrame, &Frame, sizeof(Frame));
+  readFromChild(&Frame, sizeof(Frame));
+  return Frame;
+}
+
+/// getSubprogramDesc - Return the subprogram descriptor for the current
+/// stack frame.
+const GlobalVariable *IP::getSubprogramDesc(void *Frame) const {
+  sendCommand(GetSubprogramDescriptor, &Frame, sizeof(Frame));
+  const GlobalVariable *Desc;
+  readFromChild(&Desc, sizeof(Desc));
+  return Desc;
+}
+
+/// getFrameLocation - This method returns the source location where each stack
+/// frame is stopped.
+void IP::getFrameLocation(void *Frame, unsigned &LineNo, unsigned &ColNo, 
+                          const GlobalVariable *&SourceDesc) const {
+  sendCommand(GetFrameLocation, &Frame, sizeof(Frame));
+  LocationToken Loc;
+  readFromChild(&Loc, sizeof(Loc));
+  LineNo     = Loc.Line;
+  ColNo      = Loc.Col;
+  SourceDesc = Loc.File;
+}
+
+
+//===----------------------------------------------------------------------===//
+// Breakpoint manipulation methods
+//
+unsigned IP::addBreakpoint(unsigned LineNo, unsigned ColNo,
+                           const GlobalVariable *SourceDesc) {
+  LocationToken Loc;
+  Loc.Line = LineNo;
+  Loc.Col = ColNo;
+  Loc.File = SourceDesc;
+  sendCommand(AddBreakpoint, &Loc, sizeof(Loc));
+  unsigned ID;
+  readFromChild(&ID, sizeof(ID));
+  return ID;
+}
+
+void IP::removeBreakpoint(unsigned ID) {
+  sendCommand(RemoveBreakpoint, &ID, sizeof(ID));
+}
+
+
+//===----------------------------------------------------------------------===//
+//             Methods for communication with the child process
+//
+// Methods for communicating with the child process.  If the child exits or dies
+// while attempting to communicate with it, ChildPID is set to zero and an
+// exception is thrown.
+//
+
+/// readFromChild - Low-level primitive to read some data from the child,
+/// throwing an exception if it dies.
+void IP::readFromChild(void *Buffer, unsigned Size) const {
+  assert(ChildPID &&
+         "Child process died and still attempting to communicate with it!");
+  while (Size) {
+    ssize_t Amount = read(ReadFD, Buffer, Size);
+    if (Amount == 0) {
+      // If we cannot communicate with the process, kill it.
+      killChild();
+      // If killChild succeeded, then the process must have closed the pipe FD
+      // or something, because the child existed, but we cannot communicate with
+      // it.
+      throw InferiorProcessDead(-1);
+    } else if (Amount == -1) {
+      if (errno != EINTR) {
+        ChildPID = 0;
+        killChild();
+        throw "Error reading from child process!";
+      }
+    } else {
+      // We read a chunk.
+      Buffer = (char*)Buffer + Amount;
+      Size -= Amount;
+    }
+  }
+}
+
+/// writeToChild - Low-level primitive to send some data to the child
+/// process, throwing an exception if the child died.
+void IP::writeToChild(void *Buffer, unsigned Size) const {
+  while (Size) {
+    ssize_t Amount = write(WriteFD, Buffer, Size);
+    if (Amount < 0 && errno == EINTR) continue;
+    if (Amount <= 0) {
+      // If we cannot communicate with the process, kill it.
+      killChild();
+
+      // If killChild succeeded, then the process must have closed the pipe FD
+      // or something, because the child existed, but we cannot communicate with
+      // it.
+      throw InferiorProcessDead(-1);
+    } else {
+      // We wrote a chunk.
+      Buffer = (char*)Buffer + Amount;
+      Size -= Amount;
+    }
+  }
+}
+
+/// killChild - Kill or reap the child process.  This throws the
+/// InferiorProcessDead exception an exit code if the process had already
+/// died, otherwise it just returns the exit code if it had to be killed.
+void IP::killChild() const {
+  assert(ChildPID != 0 && "Child has already been reaped!");
+  
+  int Status = 0;
+  int PID;
+  do {
+    PID = waitpid(ChildPID, &Status, WNOHANG);
+  } while (PID < 0 && errno == EINTR);
+  if (PID < 0) throw "Error waiting for child to exit!";
+
+  // If the child process was already dead, then it died unexpectedly.
+  if (PID) {
+    assert(PID == ChildPID && "Didn't reap child?");
+    ChildPID = 0;            // Child has been reaped
+    if (WIFEXITED(Status))
+      throw InferiorProcessDead(WEXITSTATUS(Status));
+    else if (WIFSIGNALED(Status))
+      throw InferiorProcessDead(WTERMSIG(Status));
+    throw InferiorProcessDead(-1);
+  }
+  
+  // Otherwise, the child exists and has not yet been killed.
+  if (kill(ChildPID, SIGKILL) < 0)
+    throw "Error killing child process!";
+
+  do {
+    PID = waitpid(ChildPID, 0, 0);
+  } while (PID < 0 && errno == EINTR);
+  if (PID <= 0) throw "Error waiting for child to exit!";
+
+  assert(PID == ChildPID && "Didn't reap child?");
+}
+
+
+/// waitForStop - This method waits for the child process to reach a stop
+/// point.  When it does, it fills in the CurLocation member and returns.
+void IP::waitForStop() {
+  char Dummy;
+  readFromChild(&Dummy, sizeof(char));
+}
+
+
+//===----------------------------------------------------------------------===//
+//                             Child Process Code
+//===----------------------------------------------------------------------===//
+
+namespace {
+  class SourceSubprogram;
+
+  /// SourceRegion - Instances of this class represent the regions that are
+  /// active in the program.
+  class SourceRegion {
+    /// Parent - A pointer to the region that encloses the current one.
+    SourceRegion *Parent;
+
+    /// CurSubprogram - The subprogram that contains this region.  This allows
+    /// efficient stack traversals.
+    SourceSubprogram *CurSubprogram;
+
+    /// CurLine, CurCol, CurFile - The last location visited by this region.
+    /// This is used for getting the source location of callers in stack frames.
+    unsigned CurLine, CurCol;
+    void *CurFileDesc;
+
+    //std::vector<void*> ActiveObjects;
+  public:
+    SourceRegion(SourceRegion *p, SourceSubprogram *Subprogram = 0)
+     : Parent(p), CurSubprogram(Subprogram ? Subprogram : p->getSubprogram()) {
+      CurLine = 0; CurCol = 0;
+      CurFileDesc = 0;
+    }
+
+    virtual ~SourceRegion() {}
+
+    SourceRegion *getParent() const { return Parent; }
+    SourceSubprogram *getSubprogram() const { return CurSubprogram; }
+
+    void updateLocation(unsigned Line, unsigned Col, void *File) {
+      CurLine = Line;
+      CurCol = Col;
+      CurFileDesc = File;
+    }
+
+    /// Return a LocationToken for the place that this stack frame stopped or
+    /// called a sub-function.
+    LocationToken getLocation(ExecutionEngine *EE) {
+      LocationToken LT;
+      LT.Line = CurLine;
+      LT.Col = CurCol;
+      const GlobalValue *GV = EE->getGlobalValueAtAddress(CurFileDesc);
+      LT.File = dyn_cast_or_null<GlobalVariable>(GV);
+      return LT;
+    }
+  };
+
+  /// SourceSubprogram - This is a stack-frame that represents a source program.
+  ///
+  class SourceSubprogram : public SourceRegion {
+    /// Desc - A pointer to the descriptor for the subprogram that this frame
+    /// represents.
+    void *Desc;
+  public:
+    SourceSubprogram(SourceRegion *P, void *desc)
+      : SourceRegion(P, this), Desc(desc) {}
+    void *getDescriptor() const { return Desc; }
+  };
+
+
+  /// Child class - This class contains all of the information and methods used
+  /// by the child side of the debugger.  The single instance of this object is
+  /// pointed to by the "TheChild" global variable.
+  class Child {
+    /// M - The module for the program currently being debugged.
+    ///
+    Module *M;
+
+    /// EE - The execution engine that we are using to run the program.
+    ///
+    ExecutionEngine *EE;
+
+    /// ReadFD, WriteFD - The file descriptor handles for this side of the
+    /// debugger pipe.
+    FDHandle ReadFD, WriteFD;
+
+    /// RegionStack - A linked list of all of the regions dynamically active.
+    ///
+    SourceRegion *RegionStack;
+
+    /// StopAtNextOpportunity - If this flag is set, the child process will stop
+    /// and report to the debugger at the next possible chance it gets.
+    volatile bool StopAtNextOpportunity;
+
+    /// StopWhenSubprogramReturns - If this is non-null, the debugger requests
+    /// that the program stops when the specified function frame is destroyed.
+    SourceSubprogram *StopWhenSubprogramReturns;
+
+    /// Breakpoints - This contains a list of active breakpoints and their IDs.
+    ///
+    std::vector<std::pair<unsigned, LocationToken> > Breakpoints;
+
+    /// CurBreakpoint - The last assigned breakpoint.
+    ///
+    unsigned CurBreakpoint;
+
+  public:
+    Child(Module *m, ExecutionEngine *ee, FDHandle &Read, FDHandle &Write)
+      : M(m), EE(ee), ReadFD(Read), WriteFD(Write),
+        RegionStack(0), CurBreakpoint(0) {
+      StopAtNextOpportunity = true;
+      StopWhenSubprogramReturns = 0;
+    }
+
+    /// writeToParent - Send the specified buffer of data to the debugger
+    /// process.
+    void writeToParent(const void *Buffer, unsigned Size);
+
+    /// readFromParent - Read the specified number of bytes from the parent.
+    ///
+    void readFromParent(void *Buffer, unsigned Size);
+
+    /// childStopped - This method is called whenever the child has stopped
+    /// execution due to a breakpoint, step command, interruption, or whatever.
+    /// This stops the process, responds to any requests from the debugger, and
+    /// when commanded to, can continue execution by returning.
+    ///
+    void childStopped();
+
+    /// startSubprogram - This method creates a new region for the subroutine
+    /// with the specified descriptor.
+    void startSubprogram(void *FuncDesc);
+
+    /// startRegion - This method initiates the creation of an anonymous region.
+    ///
+    void startRegion();
+
+    /// endRegion - This method terminates the last active region.
+    ///
+    void endRegion();
+
+    /// reachedLine - This method is automatically called by the program every
+    /// time it executes an llvm.dbg.stoppoint intrinsic.  If the debugger wants
+    /// us to stop here, we do so, otherwise we continue execution.
+    void reachedLine(unsigned Line, unsigned Col, void *SourceDesc);
+  };
+
+  /// TheChild - The single instance of the Child class, which only gets created
+  /// in the child process.
+  Child *TheChild = 0;
+} // end anonymous namespace
+
+
+// writeToParent - Send the specified buffer of data to the debugger process.
+void Child::writeToParent(const void *Buffer, unsigned Size) {
+  while (Size) {
+    ssize_t Amount = write(WriteFD, Buffer, Size);
+    if (Amount < 0 && errno == EINTR) continue;
+    if (Amount <= 0) {
+      write(2, "ERROR: Connection to debugger lost!\n", 36);
+      abort();
+    } else {
+      // We wrote a chunk.
+      Buffer = (const char*)Buffer + Amount;
+      Size -= Amount;
+    }
+  }
+}
+
+// readFromParent - Read the specified number of bytes from the parent.
+void Child::readFromParent(void *Buffer, unsigned Size) {
+  while (Size) {
+    ssize_t Amount = read(ReadFD, Buffer, Size);
+    if (Amount < 0 && errno == EINTR) continue;
+    if (Amount <= 0) {
+      write(2, "ERROR: Connection to debugger lost!\n", 36);
+      abort();
+    } else {
+      // We read a chunk.
+      Buffer = (char*)Buffer + Amount;
+      Size -= Amount;
+    }
+  }
+}
+
+/// childStopped - This method is called whenever the child has stopped
+/// execution due to a breakpoint, step command, interruption, or whatever.
+/// This stops the process, responds to any requests from the debugger, and when
+/// commanded to, can continue execution by returning.
+///
+void Child::childStopped() {
+  // Since we stopped, notify the parent that we did so.
+  char Token = 0;
+  writeToParent(&Token, sizeof(char));
+
+  StopAtNextOpportunity = false;
+  StopWhenSubprogramReturns = 0;
+
+  // Now that the debugger knows that we stopped, read commands from it and
+  // respond to them appropriately.
+  CommandID Command;
+  while (1) {
+    SourceRegion *Frame;
+    const void *Result;
+    readFromParent(&Command, sizeof(CommandID));
+
+    switch (Command) {
+    case StepProgram:
+      // To step the program, just return.
+      StopAtNextOpportunity = true;
+      return;
+
+    case FinishProgram:         // Run until exit from the specified function...
+      readFromParent(&Frame, sizeof(Frame));
+      // The user wants us to stop when the specified FUNCTION exits, not when
+      // the specified REGION exits.
+      StopWhenSubprogramReturns = Frame->getSubprogram();
+      return;
+
+    case ContProgram:
+      // To continue, just return back to execution.
+      return;
+
+    case GetSubprogramDescriptor:
+      readFromParent(&Frame, sizeof(Frame));
+      Result =
+        EE->getGlobalValueAtAddress(Frame->getSubprogram()->getDescriptor());
+      writeToParent(&Result, sizeof(Result));
+      break;
+
+    case GetParentFrame:
+      readFromParent(&Frame, sizeof(Frame));
+      Result = Frame ? Frame->getSubprogram()->getParent() : RegionStack;
+      writeToParent(&Result, sizeof(Result));
+      break;
+
+    case GetFrameLocation: {
+      readFromParent(&Frame, sizeof(Frame));
+      LocationToken LT = Frame->getLocation(EE);
+      writeToParent(&LT, sizeof(LT));
+      break;
+    }
+    case AddBreakpoint: {
+      LocationToken Loc;
+      readFromParent(&Loc, sizeof(Loc));
+      // Convert the GlobalVariable pointer to the address it was emitted to.
+      Loc.File = (GlobalVariable*)EE->getPointerToGlobal(Loc.File);
+      unsigned ID = CurBreakpoint++;
+      Breakpoints.push_back(std::make_pair(ID, Loc));
+      writeToParent(&ID, sizeof(ID));
+      break;
+    }
+    case RemoveBreakpoint: {
+      unsigned ID = 0;
+      readFromParent(&ID, sizeof(ID));
+      for (unsigned i = 0, e = Breakpoints.size(); i != e; ++i)
+        if (Breakpoints[i].first == ID) {
+          Breakpoints.erase(Breakpoints.begin()+i);
+          break;
+        }
+      break;
+    }
+    default:
+      assert(0 && "Unknown command!");
+    }
+  }
+}
+
+
+
+/// startSubprogram - This method creates a new region for the subroutine
+/// with the specified descriptor.
+void Child::startSubprogram(void *SPDesc) {
+  RegionStack = new SourceSubprogram(RegionStack, SPDesc);
+}
+
+/// startRegion - This method initiates the creation of an anonymous region.
+///
+void Child::startRegion() {
+  RegionStack = new SourceRegion(RegionStack);
+}
+
+/// endRegion - This method terminates the last active region.
+///
+void Child::endRegion() {
+  SourceRegion *R = RegionStack->getParent();
+
+  // If the debugger wants us to stop when this frame is destroyed, do so.
+  if (RegionStack == StopWhenSubprogramReturns) {
+    StopAtNextOpportunity = true;
+    StopWhenSubprogramReturns = 0;
+  }
+
+  delete RegionStack;
+  RegionStack = R;
+}
+
+
+
+
+/// reachedLine - This method is automatically called by the program every time
+/// it executes an llvm.dbg.stoppoint intrinsic.  If the debugger wants us to
+/// stop here, we do so, otherwise we continue execution.  Note that the Data
+/// pointer coming in is a pointer to the LLVM global variable that represents
+/// the source file we are in.  We do not use the contents of the global
+/// directly in the child, but we do use its address.
+///
+void Child::reachedLine(unsigned Line, unsigned Col, void *SourceDesc) {
+  if (RegionStack)
+    RegionStack->updateLocation(Line, Col, SourceDesc);
+
+  // If we hit a breakpoint, stop the program.
+  for (unsigned i = 0, e = Breakpoints.size(); i != e; ++i)
+    if (Line       == Breakpoints[i].second.Line &&
+        SourceDesc == (void*)Breakpoints[i].second.File &&
+        Col        == Breakpoints[i].second.Col) {
+      childStopped();
+      return;
+    }
+
+  // If we are single stepping the program, make sure to stop it.
+  if (StopAtNextOpportunity)
+    childStopped();
+}
+
+
+
+
+//===----------------------------------------------------------------------===//
+//                        Child class wrapper functions
+//
+// These functions are invoked directly by the program as it executes, in place
+// of the debugging intrinsic functions that it contains.
+//
+
+
+/// llvm_debugger_stop - Every time the program reaches a new source line, it
+/// will call back to this function.  If the debugger has a breakpoint or
+/// otherwise wants us to stop on this line, we do so, and notify the debugger
+/// over the pipe.
+///
+extern "C"
+void *llvm_debugger_stop(void *Dummy, unsigned Line, unsigned Col,
+                         void *SourceDescriptor) {
+  TheChild->reachedLine(Line, Col, SourceDescriptor);
+  return Dummy;
+}
+
+
+/// llvm_dbg_region_start - This function is invoked every time an anonymous
+/// region of the source program is entered.
+///
+extern "C"
+void *llvm_dbg_region_start(void *Dummy) {
+  TheChild->startRegion();
+  return Dummy;
+}
+
+/// llvm_dbg_subprogram - This function is invoked every time a source-language
+/// subprogram has been entered.
+///
+extern "C"
+void *llvm_dbg_subprogram(void *FuncDesc) {
+  TheChild->startSubprogram(FuncDesc);
+  return 0;
+}
+
+/// llvm_dbg_region_end - This function is invoked every time a source-language
+/// region (started with llvm.dbg.region.start or llvm.dbg.func.start) is
+/// terminated.
+///
+extern "C"
+void llvm_dbg_region_end(void *Dummy) {
+  TheChild->endRegion();
+}
+
+
+
+
+namespace {
+  /// DebuggerIntrinsicLowering - This class implements a simple intrinsic
+  /// lowering class that revectors debugging intrinsics to call actual
+  /// functions (defined above), instead of being turned into noops.
+  struct DebuggerIntrinsicLowering : public DefaultIntrinsicLowering {
+    virtual void LowerIntrinsicCall(CallInst *CI) {
+      Module *M = CI->getParent()->getParent()->getParent();
+      switch (CI->getCalledFunction()->getIntrinsicID()) {
+      case Intrinsic::dbg_stoppoint:
+        // Turn call into a call to llvm_debugger_stop
+        CI->setOperand(0, M->getOrInsertFunction("llvm_debugger_stop",
+                                  CI->getCalledFunction()->getFunctionType()));
+        break;
+      case Intrinsic::dbg_region_start:
+        // Turn call into a call to llvm_dbg_region_start
+        CI->setOperand(0, M->getOrInsertFunction("llvm_dbg_region_start",
+                                  CI->getCalledFunction()->getFunctionType()));
+        break;
+
+      case Intrinsic::dbg_region_end:
+        // Turn call into a call to llvm_debugger_stop
+        CI->setOperand(0, M->getOrInsertFunction("llvm_dbg_region_end",
+                                  CI->getCalledFunction()->getFunctionType()));
+        break;
+      case Intrinsic::dbg_func_start:
+        // Turn call into a call to llvm_debugger_stop
+        CI->setOperand(0, M->getOrInsertFunction("llvm_dbg_subprogram",
+                                  CI->getCalledFunction()->getFunctionType()));
+        break;
+      default:
+        DefaultIntrinsicLowering::LowerIntrinsicCall(CI);
+        break;
+      }
+    }
+  };
+} // end anonymous namespace
+
+
+static void runChild(Module *M, const std::vector<std::string> &Arguments,
+                     const char * const *envp,
+                     FDHandle ReadFD, FDHandle WriteFD) {
+
+  // Create an execution engine that uses our custom intrinsic lowering object
+  // to revector debugging intrinsic functions into actual functions defined
+  // above.
+  ExecutionEngine *EE =
+    ExecutionEngine::create(new ExistingModuleProvider(M), false,
+                            new DebuggerIntrinsicLowering());
+  assert(EE && "Couldn't create an ExecutionEngine, not even an interpreter?");
+  
+  // Call the main function from M as if its signature were:
+  //   int main (int argc, char **argv, const char **envp)
+  // using the contents of Args to determine argc & argv, and the contents of
+  // EnvVars to determine envp.
+  //
+  Function *Fn = M->getMainFunction();
+  if (!Fn) exit(1);
+
+  // Create the child class instance which will be used by the debugger
+  // callbacks to keep track of the current state of the process.
+  assert(TheChild == 0 && "A child process has already been created??");
+  TheChild = new Child(M, EE, ReadFD, WriteFD);
+
+  // Run main...
+  int Result = EE->runFunctionAsMain(Fn, Arguments, envp);
+
+  // If the program didn't explicitly call exit, call exit now, for the program.
+  // This ensures that any atexit handlers get called correctly.
+  Function *Exit = M->getOrInsertFunction("exit", Type::VoidTy, Type::IntTy, 0);
+
+  std::vector<GenericValue> Args;
+  GenericValue ResultGV;
+  ResultGV.IntVal = Result;
+  Args.push_back(ResultGV);
+  EE->runFunction(Exit, Args);
+  abort();
+}